1. Field of the Invention
This invention relates to a temperature measuring device, a thermal processor having a temperature measurement function and a temperature measurement method, and for example, to a device and method for measuring temperature of a heating plate for use in heating wafers.
2. Description of Background Art
In a photolithography process during the manufacture of semiconductor devices, various thermal treatments, including a heat treatment (pre-bake) which is performed after the application of resist solution onto a surface of a semiconductor wafer (hereinafter referred to as “wafer”), a heat treatment (post-exposure-bake) which is performed after exposing patterns, and a cooling treatment which is performed after each heat treatment, are carried out by, for instance, a heating/cooling system capable of maintaining the wafer at a predetermined temperature.
FIG. 15 is a vertical cross-sectional view of a conventional heating/cooling system 60, while FIG. 16 is a transverse sectional view taken along lines A-A of FIG. 15.
FIG. 15 shows that a heating/cooling system 60 has an enclosure 90 including therein a cooling plate 61 for use in cooling wafers and a heating plate 62 for use in heating wafers juxtaposed to the cooling plate 61. The cooling plate 61 and heating plate 62 are discs with a certain thickness. The cooling plate 61 incorporates some devices such as a Peltier device (not shown) for cooling the cooling plate 61 to a predetermined temperature.
Under the cooling plate 61 provided are elevator pins 63 for supporting and moving up and down the wafer to mount the wafer on the cooling plate 61. These elevator pins 63, which can be moved upward and downward by a vertical drive mechanism 64, are configured to penetrate the cooling plate 61 from the bottom so as to protrude through the upper surface of the cooling plate 61.
On the other hand, the heating plate 62 incorporates a heater 65 and a heating-plate temperature sensor 62a. The temperature of the heating plate 62 is maintained at a preset temperature by a controller 66 that controls the heating value of the heater 65 based on the temperature sensed by the heating-plate temperature sensor 62a. As with the cooling plate 61, elevator pins 67 and a vertical drive mechanism 68 are provided under the heating plate 62. These elevator pins 67 allow the wafer to be mounted on the heating plate 62.
As shown in FIG. 15, a transfer device 69 is disposed between the cooling plate 61 and heating plate 62 to transfer a wafer to the heating plate 62 and to transfer the wafer from the heating plate 62 to the cooling plate 61. A transfer opening 70 is formed in the enclosure 90 of the heating/cooling system 60 and adjacent to the cooling plate 62, for bringing the wafer in and taking the wafer out of the heating/cooling system 60.
In addition, this transfer opening 70 is attached with a shutter 71 to maintain an atmosphere in the heating/cooling system 60 to have a predetermined one. A transfer arm 80, which is placed opposite the shutter 71, transfers the wafer through the transfer opening 70 when the shutter 71 is opened. The transferred wafer is further transferred by the transfer device 69 onto the heating plate 62.
By using such a heating/cooling system 60, it is important to measure temperature distribution of the wafer mounted on the heating plate 62 in advance to grasp temperature characteristics of the wafer on the heating plate 62 and to heat the wafer on the heating plate 62 uniformly with appropriate compensation based on the results. In order to measure the temperature distribution of the wafer on the heating plate 62, temperature measuring devices have been conventionally used to grasp the temperature distribution of the wafer and adjust the temperature distribution before the actual treatment of the wafer.
FIG. 17A and 17B illustrate some examples of the conventional temperature measuring device. An example shown in FIG. 17A comprises a wafer K for use in measuring temperature, which is made of the same material and in the same shape as the real semiconductor wafer, a plurality of temperature sensors 101 spread over the temperature-measuring wafer K to detect temperatures with the use of thermocouples or the like, and a transmitting device 103. The temperature sensors 101 are connected to the transmitting device 103 through cables 102. Data detected by each temperature sensor 101 is sent from the transmitting device 103 by radio and then received by a receiving device disposed inside or outside the heating/cooling system 60. Because the temperature data detected by each temperature sensor 101 is represented by analog values, the transmitting device 103 needs to incorporate an AID converter to convert the analog temperature data into digital data. However, the A/D converter that deteriorates conversion accuracy with an increase in temperature may be able to be used to measure temperatures up to about 150 degrees C., but can not be used in the atmosphere at temperatures rising to 250 degrees C.
Japanese unexamined patent publication No. 2002-124457 discloses another example as shown in FIG. 17B in which the transmitting device 103 shown in FIG. 15A is disposed on a disc S that is prepared in addition to the temperature-measuring wafer K and each temperature sensor 101 on the temperature-measuring wafer K is connected to the transmitting device 103 via cables 102. Since this example is configured to mount only the temperature-measuring wafer K on the heating plate 62 and to locate the disc S above the temperature measuring wafer K with a distance therebetween, the A/D converter can keep a distance from the heating plate 62, and therefore the A/D converter incorporated in the transmitting device 103 is prevented from accuracy deterioration caused by high temperatures.
However, the temperature-measuring wafer K with the disc S located thereabove causes difficulty in transferring wafers with the transfer device 69 and transfer arm 80 shown in FIG. 16, thus requiring a specially prepared transfer device and transfer arm.
Alternatively, Japanese unexamined patent publication No. 2004-150860 discloses another example of the temperature measuring device using a surface acoustic wave device (hereinafter referred to as “SAW device”). As shown in FIG. 18, this example comprises antenna sections 111 and a SAW device 113 including an excitation electrode 112 connected to the antenna sections 111 in a package body 110 made of a dielectric material. This publication discloses that with the use of the characteristics of the SAW device 113 which generates surface acoustic waves having a propagation velocity that is variable depending on temperature, temperature is determined by measuring how long the reflected surface acoustic wave take to return and calculating from temperature delay of the SAW device 113 in an arithmetic circuit at a base station.
In order to uniformly heat wafers with the heating/cooling system 60 shown in FIG. 15, automated measurement of the temperature distribution of a wafer mounted on the heating plate 62 is required. In the example using the SAW device 113 shown in FIG. 18, however, it may be possible to measure temperature of a certain region of the wafer, but is impossible to measure temperature distribution at various regions of the wafer. Even if the SAW device 113 is replaced with the temperature sensors 101 shown in FIGS. 17A and 17B, temperature measurement of various regions on a wafer cannot be achieved because the reflected frequency waves of the temperature sensors 101 interfere with each other.